Electrical steels and method of making same



Oct. 24, 1933.

E. M. FREELAND ELECTRICAL STEELS AND METHOD OF MAKING SAME Filed Feb.18, 1932 0 0 0 0 0 W 0 o o m w 2 2 z Z M m 6 9 L Elo' INVENTOR W7Patented Oct. 24, 1933 UNITED STATES ELECTRICAL STEELS AND METHOD OF 1MAKING SAME Edward M. Freeland, Pittsburgh, Pa.

Application February 18,

, 15 Claims.

The present invention relates broadly to the art of metal working, andmore especially to that branch of metal working having to do with thesubjecting of a predetermined composition or alloy to a treatment ofsuch nature that the electrical properties thereof are materiallymodified.

In an effort to improve the efficiency of different types of electricalapparatus, such for example as motors, dynamos, transformers and thelike, it is customary to utilize a ferrous material, usually in the formof a series of sheets or laminae characterized by a high electricalefnciency from the standpoint for example of watt loss, magneticpermeability, low magnetic hysteresis and the like. In this connectionit is known that sheets of iron-silicon, or iron-silicon-aluminum alloysconstitute a superior material for this purpose. The present inventioncontemplates not only a variation in the constituent alloys utilized asto their relative proportions for obtaining certain predeterminedresults as required for example by the apparatus in which the finishedproduct is to be used, but also a special mechanical and heat treatmentwhereby with a given material the desired electrical properties areimparted thereto.

It is customary in the art to divide so-called electrical steels into anumber of different grades generally with reference to the particularuse to which the steels are to be put. It is to be understood,therefore, that the term electrical steels as hereinafter utilized,unless specifically restricted to a specified grade by way of example,is to be considered as a generic term including all of the variousgrades without regard to the specific properties or uses contemplated.

For purposes of a better understanding of the invention, it willhereinafter be illustrated and described as applicable to a ferrousmaterial, preferably containing silicon, having a low watt loss andproduced initially from so-called strip material, the term strip beingherein utilized in its commonly accepted sense in the metal roll ingart. 7

Experience in the production or electrical steels of the characterherein contemplated has led to the conclusion that the desiredelectrical properties can be obtained only bya treatment which includesas one of the steps thereof a cold working operation, preferably in theform of cold rolling. It has heretofore been considered essen- 1932.Serial No. 593,783

tial to so effect the cold working or cold rolling operation as todefinitely limit the maximum strain introduced into the material, itbeing understood that the reduction effected by the cold workingoperation necessarily determines the amount of strain introduced. Thenecessity of maintaining the strain so introduced below definite maximumlimits has heretofore precluded the use of the cold working process formaterial in strip form for the reason that in cold rolling a hot rolledstrip to gauge, the strain introduced has far exceeded the upper limitspermissible at any. stage in the manufacture of electrical steels. Theamount of reduction by cold work has heretofore been limited to amaximum of 540%, which is so small as to be of little consequence so faras concerns merely the step of cold rolling to reduce thickness.

The present invention is preferably characterized by the step ofdeliberately introducing a strain by cold rolling in excess of anylimits heretofore considered permissible, and thereafter subjecting thematerial having such excessive strain therein to a controlled treatmentsuch that the strain in excess of the maximum limit is effectivelyremoved, and only the desired strain for imparting the requiredelectrical properties is retained. In this manner I retain only thatamount of strain which has heretofore been determined .as beingdecidedly beneficial, and make the process adaptable to the productionin quantity of electrical steels. The adaptation to the strip processalso enables the production of a product having materially greaterlengths than has heretofore been possible, and thereby correspondinglyreducing the fabricating costs in the manufacture of electricalapparatus. This will be readily apparent when it is considered that itis entirely possible to produce, in accordance with my invention, thedesired grade of electrical steel in strip form having a length, forexample, in the neighborhood of 1000 ft., and capable of being autornatically fed to a suitable punch or the like such as utilized in thefabrication. of the ma terial. Heretofore electrical steels could onlybe produced in lengths not to exceed approximately 15 ft. Suchindividual pieces required individual handling and feeding to thepunches and the like, and therefore required the constant attend ance ofan operator.

The present invention therefore has for one of its objects an improvedmethod of producing electrical steel, as well as the production of a newarticle of manufacture comprising electrical steel in strip form havinga length in excess of lengths heretofore obtainable from sheets asindividually produced.

In the acompanying drawing I have shown more or less diagrammatically,by way of illustration only, certain preferred embodiments of thepresent invention. In the drawing:-

Figure 1 is a diagrammatic view, partly in side elevation, illustratingthe various treatment steps to which strip material may be subjected inaccordance with the present invention;

Figure 2 illustrates a modified method of heat treating materialproduced in accordance with the present invention;

Figure 3 is a chart illustrating one method of effecting partial strainremoval prior to final heat treatment; 7

Figure 4 is a diagrammatic view, partly in side elevation, illustratinga slightly modified form of treatment from that shown in Figure 1; and

Figure 5 is a view similar to Figure 4, illustrating still anotherembodiment of my invention.

While it will be understood that Figures 1, 4 and 5, respectively,illustrate diiferent manipulative steps, processes or treatments towhich the material is subjected in attaining the desired results, as thedescription proceeds, the relevancy of the different steps to theinvention will become more clearly apparent.

Having reference more particularly to Figure 1 of the drawing, I haveshown a slab 2 of desired composition suitable for use in accordancewith the present invention. This slab is subjected to hot rolling, ascommonly practiced in the art in a suitable series of hot rolling mills3 of such nature as to form a hot rolled strip, herein illustrated inthe form of a coil 4. It may be assumed, by way of example only, thatthe hot rolled strip thus pro-- duced and which is substantially freefrom any cold working strains, has a thickness of .0625 inches, and anydesired width. I prefer to use a minimum finishing temperature ofapproximately 1300 F. This hot rolled strip, in accordance with thepresent invention, is subjected to a cold rolling operation in acontinuous mill 5, herein illustrated as comprising four roll stands ofthe four-high type arranged in tandem.

By way of illustration only, it may be further assumed that the settingof the cold rolling mills is such as to reduce the thickness of the hotrolleTi strip to approximately .024 inches, this being a reduction of.0385 inches, equal to approximately 61%. It will be apparent to thoseskilled in the art that the figures herein given are representative ofthicknesses frequently produced in the cold rolling of steel forpurposes other than the production of electrical steels.

The cold rolling operation, while it is effective for reducing the hotrolled strip to the desired finished gauge, introduces in such materialby reason of the reduction effected, a strain which is far in excess ofthe strain heretofore thought permissible in the production of steels tobe used for electrical purposes. In accordance with the presentinvention, however, I take advantage of the strain introduction effectedby such a cold rolling operation, and consider such strain asrepresenting a desirable component and an undesirable component. Inaccordance with the present invention, the strip having these two straincomponents is subjected to a special heat treating operation of suchnature as to retain the desirable component and eliminate theundesirable component.

It may be assumed that the strip leaving the cold rolling mill 5 isformed into a coil 6 for convenience in handling. This coil is thenplaced in a suitable coil b x '7 located in the de sired relationship tothe charging end of a heat treating furnace 8 provided with suitableburners or resistors 9 effective for maintaining the desired temperatureconditions therein. The coil 6 is progressively unwound from the coilbox 7 and passed in single thickness through the furnace 8 at a speedwhich is determined not only upon the temperature conditions existingwithin the furnace, but also upon the composition of the materialundergoing treatment, the thickness of such material and the amount ofstrain introduced therein by the cold rolling operation. Upon leavingthe heat treating zone provided by the furnace 8, the strip material mayagain be formed into a coil 10, which will be characterized, as will behereinafter more fully explained, by the elimination of the undesirablestrain component and will have only the desirable strain componentremaining therein. This coil may then be subjected to a final heattreating operation as by subjecting it to a box annealing operation incoil form in an annealing box 11. Upon removal from the annealing box,the strip material in coil form may be sold as an article of manufacturefor use in the fabricating of electrical equipment, or may be cut intoindividual sheets and so sold for fabrication. When retained in coilform it is possible to obtain all of the advantages hereinbeforereferred to with respect to use in automatic fabricating machines with aminimum of expense, attention and handling.

In other cases, the coil 10 as formed at the delivery end of the heattreating furnace 8 may be sheared into individual sheets 12, whichsheets when placed in superimposed relationship as illustrated in Figure2, may be subjected to a box annealing operation in a suitable annealingbox 14. After the desired annealing operation, the sheets 12 as such maythen be sold for use.

Reference has heretofore been made to a cold rolling operation effectivefor producing a reduction of approximately 61%. If this reduction iseffected on strip having a relatively low silicon content, say forexample approximately 1%, it will be found that the resulting strain inthe strip is appreciably less than the strain which will result fromexactly the same reduction on a steel having for example, approximately2% silicon. It must therefore be borne in mind that the unde sirablestrain component increases in amount as the silicon content of thematerial undergoing treatment increases, with the same percentagereduction by the cold mill.

With any given silicon content, the undesirable strain component willlikewise vary with changes in the reduction effected by the cold rollingoperation, the strain increasing with increased reductions anddecreasing with decreased reductions. While the actual strain introducedunder varying reductions is not a straight line function, it is afunction which is readily deter minable.

In practicing my invention I have successfully employed a continuousheating furnace as indicated at 8 in Figure 1. The furnace had a lengthof 30 feet and was maintained at a temperature of approximately 1900 F.Silicon steel strip containing approximately 1% of silicon, which steelhad been subjected to a 61% reduction by cold rolling and having a finalthickness of .025 inches was passed through the furnace at a rate of 15feet per minute, giving a total time in the furnace of two minutes. Ihave estimated that in the particular furnace employed the heatpenetrated sufiiciently rapidly to bringthe strip up to the desiredminimum temperature in approximately seconds. The additional 90 secondsof heating time was available for continued heating. Under the aboveconditions the heat treatment eliminated the undesirable straincomponent and left the desirable strain components therein.

In Figure 3 I have illustrated diagrammatically by the point A on thecurve the particular heat treatment above described. The curve of Figure3 is obtained by plotting the thickness of the material against theheating time in seconds. It is generally assumed that the rate of heatpenetration varies directly with the thickness of the material; andhence if the strip being treated were only half as thick, that is tosay, .0125 inches, then only 15 seconds would be required to bring it upto the desired minimum temperature. Adding to this the continued heatingtime of 90 seconds, the total time for treating such strip would be 105seconds. This condition is indicated by the point B on the curve. Asstated, if, as is generally assumed, the rate of heat penetration variesdirectly with the thickness of the material, the curve for determiningthe length of time for treating strips of different thicknesses will bea straight line connecting the points A and B. The points C, D, E and Fhave been marked on this line in Figure 3 to show the time required forheat treating strips having thicknesses, respectively, of .014, .016,.018 and .020 inches.

The above described curve is for steel having a silicon content ofapproximately 1% and which has been reduced approximately 61% by coldrolling. It sets forth the general principle of treatment to be followedin the continuous heat treatment of such strip for the elemination ofthe undesirable strain component, but it will be understood that thecurve is by way of example only; that modifications in the heattreatment may be made; that the customary tolerances in mill practiceare allowable, and that the percentage of reduction by cold rolling maybe varied according to the particular circumstances encountered and theresults desired.

In accordance with the' present invention, it is permissible to considerthe heat treating operation by means of which the undesirable straincomponent is eliminated as involving two factors, these beingrespectively, time and temperature. If it is desired to decrease thetime of treatment, it is necessary to eifect an increase in thetemperature, while if it is desired to increase the time interval, thismay be accomplished by effecting a reduction in the temperatureconditions. The examples given therefore are by way of illustration ofactual times required for a given temperature condition, it beingpossible in accordance with the invention to vary either the time ortemperature by making a corresponding change as indicated in the otherheat treating factor.

In like manner, since the undesirable strain component introduced intothe material increase with higher silicon contents, and decrease as thesilicon content is reduced, it is necessary to make a correspondingchange in the time-temperature treatment to accommodate the treatment tothe silicon content present in the material. In substantially the sameway, it is also necessary where the percentage of reduction varies,either upwardly or downwardly, to effect a corresponding change upwardlyor downwardly of the timetemperature treatment, it being remembered thatin all cases the minimum. or desirable strain component is to beretained in the material and only the excess or undesirable straincomponent eliminated.

The present invention will thus be found to be applicable commerciallyto the cold rolling of silicon steel in strip form in direct accordancewith the past commercial practices determined for cold rollingoperations generally as applicable to products other than ferrousmaterials for elec- 'trical purposes, thus enabling commercialinstallations to be utilized for carrying out the present invention. Y

I have found that, depending upon the properties desired in the finishedproduct, and effective uses to which such product is to be put, or, inother words, depending upon the grade of material to be produced, thesilicon content may be varied through appreciable limits. As a generalstatement, it may be assumed that a silicon content of approximately 1%is desirable for example in the production of that grade of materialknown generally as electrical sheets; that a silicon content ofapproximately 2 5% is desirable for the production at that grade ofmaterial commonly referred to as special motor sheets; that a siliconcontent of approximately 3% is desirable for the production of thatgrade of material commonly referred to as special dynamo sheets, andthat a silicon content of approximately 3 5% produces the desiredproperties for use in so-called transformer sheets. Inasmuch, however,as the determining factor in the different grades referred to is theactual watt loss per 1b., determined in accordance with lmown methods,and such watt losses are themselves subject to change, the figures andgrades given must be considered as illustrative only. It will likewisebe understood that the approximate percentages of silicon are notabsolute, it being possible to utilize a silicon content varying forexample, as much as 5% in one direction or the other and still obtaindesirable results with the present invention. 1 have referred to 3%;%merely by way of example, as the upper limit of silicon. It is to beunderstood, however, that the actual amount of silicon present may bematerially increased, as for example, up to approximately 6% if such ahigher silicon content is desired, by reason of changes in the watt lossrequirements or guarantees of the manufacturer.

All of the material produced in accordance with the present inventionwill be characterized by having a relatively low watt loss at a givenflux density. As an example of guarantees which it is possible to meet,there is given below a table containing seven difierent grades ofelectrical steel, each with an identifying title together with the wattloss per lb. at frequencies of both and cycles at the assumed specificgravities indicated, the maximum watt losses in the case of some of thegrades being shown for a plurality of different gauges, these rangescovering the gauges ordinarily manufactured. In all cases the watt lossis figured at a flux density of 10,000-B and determined in accordancewith specification A-3428 of the American Society for Testing Materials.In each instance I have also indicated one permissible range of siliconvariation for each grade:

Armature (Assumed sp. gr. 7.70)

8 Silicon .S-J-U. S. atandard gauge: 0

30 G. 29 Cl. 28 G. 27 G. 20 G 25 G. 24 G. 23 G. 22 G.

\Vntts per lb.--60 cycles 1. 85 l. 40 1. 46 1. 53 1. (l5 1. 85 2.15 2.50 2. B0 \Vatts per kg.--60 cycles. 2. 97 3. 08 3. 20 3. 37 3. G3 4. 074. 73 5. 50 6. l5 \Vatls per lb.-5O cycles- 1.12 1. 17 1. 20 1. 30 1.42 1. 53 1. 75 2. 00 2. 30 Watts per kg.-50 cycles... 2. 4.6 2. 57 2. 642. 86 3. 12 3. 37 3. 4. 40 5. ()5

Electrical (Assumed sp. gr. 7.70)

Silicon .75-1.6- U. 8. standard gauges Watts per lb.60 cycles.-- 1.15 l.20 1. 28 l. 35 1. 40 1. 55 1. 80 2.10 2. 39 Watts per kg.60 cycles- 2.53 2. 64 2. 82 2. 97 3. 08 3. 41 3. 9G 1. 02 5. 06 Watts per lb.50cycles l. 00 l. 07 1.14 1.18 l. 30 1. 50 l. 70 l. 85 'atts per kg.-50cycles. 2. 09 2. 20 2. 3 2. 51 2. 60 2. 86 3. 30 3. 7-1 1. 07 9 r aSpecial motor (Assumed sp. gr. 7.50)

Silicon B.03.0U. 5. standard gauges Watts per Ib.-(l0 cycles 1.00 I1.03 1. 08 1. 15 I 1 20 1. 25 1.110 1011'} Watts per kg.-(i0 cycles. 2.20 2. .27 2, 38 2. 5.5 2. 64 2. 75 2. ill; Watts pcr lb.5l) cycles....81 .86 90 .9 1 .97 1.110 1.05 Watts per kg.50 cycles H 1.85 1 81') l 982 0T 2. l3 2. 2i) 2. 3]

Special dynamo (Assumed 51). 5:1. .50)

Silicon .-2..-5-s.5- U. s. slamlarrl /u Watts per lb.60 cycles Watts perkg.60 cycles Watts pcr ilL-SU cycllcs. 1 atts )er ,.50 c '0 es 1.98 l rs I I I 1M Regular transformer (Assumed m yr. 7.50)

Silicon 3 pZus-U. S. sirmdm u lmy m Watts per 1h. -c0 cycles 7n so l .99.03 93 Vt'zltts per kgr-GO cycles 1. (i7 1. 76 1. 87 1. 96 2. 05 2. 16Watts per lb.-50 cycles. 62 61 .158 71 75 78 Watts per kg.-5(l cycles1.375 I l. 41 1.50 1. 56 1. 65 l. 72

Special transformer (Assumed sp. gr. 7.50)

Silicon 8% plus I Watts per lb.-60 cycles 70 Watts per kg.60 cycles. 1.54 Watts per lb.-50 cycles.-- 56 Watts per kg.50 cycles 1. 24

Extra special transformer (Assumed sp. gr. 7.50)

Silicon 8% plus Watts per lb.-6O cycles. 61 Watts per kg.-60 cycles. 1.42 Watts per lb.50 cycles. 52 Watts per kg.-50 cycles. l. 15

From the foregoing tables it will be noted that my improved electricalstrip has 9. watt loss not exceeding 2.8 per pound in 22 gauge stripcontaining .3 to .'7% silicon and that the watt loss decreasesprogressively as the silicon content increases, within the range hereindisclosed, and also decrease with a decrease in thickness of the strip.

With the embodiment of the invention illustrated more particularly inFigure 1 of the drawing, it will be understood that the coil material asdelivered by the annealing box 11 for example, will have a coil setwhich will be reflected in the individual pieces formed therefrom.Inasmuch slight curvature reflected in the individual lamina may beobjectionable. In accordance with the embodiment of Figure 2, the coilset may be eliminated, but in this case it is not possible to furnish toa customer a material in coil form .with its consequent advantages. Incases where the advantages of a coil without the objection as to coilset are required, I may practice a method as illustrateddiagrammatically in Figure 4.

In this figure, I have shown a furnace 15 indicated as being a bell typeelectric furnace characterized by the ability to closely controltemperature conditions. I may place within such furnace a coil producedin any desired manner, such for example as the product of the cold roll-.ing mill 5 of Figure 1 and subject the coil to such accuratelycontrolled heat treating conditions as to efiect removal only of theundesirable strain component;

Thereafter tlriis coil may be placed in a suitable coil box 16 andpassed through a heat treating furnace 17 corresponding to the furnace 8of Figure l and effective for giving the final heat treatment to thematerial. Instead of coiling the material at a point closely adjacentthe top of the furnace 1'7, I may carry it to a point ap-.

preciably removed therefrom before forming it into a coil 18. Thelocation of the coil 18 relatively to the furnace 17 will be such thatthe material will have cooled to such an extent that it will not have atendency even when coiled to take a coil set, but will always tend toreturn to its substantially fiat condition.

In Figure 5, I have also illustrated one method of practicing theinvention means of which the desired results may be obtained. In thisfigure, I have shown an annealing box 19 having coils of material 20therein. These coils may be the product either of a cold rolling mill asshown in Figure l, or of the usual hot mill. In the annealing box theyare subjected to a suitable heat treating operation. Upon removal fromthe annealing box the coils may be placed in a suitable coil box 21 andfed therefrom between rolls 22 of a suitable mill effective forintroducing a desired strain component into the material to the extentrequired to impart the desired electrical properties. Thereafter thematerial with this strain, representing only the desirable strain component, may be passed through a furnace 23 corresponding to the furnaces 8and 1'7, and then at a suitably remote point coiled into a coil 24. Inthis coil 24 the material will possess the same attributes as thematerial in coil 18 of Figure 4.

In accordance with the embodiments of the invention of Figures 4 and 5,it is possible to produce as an article of manufacture a coil ofelectrical strip wherein the strip itself is substantially free from anyobjectionable coil set of the character referred to.

It will be understood that when practicing the form of the inventionshown in Figures 1 and 2, the annealing box temperatures will be such asto effect final removal of the strain. I have found that thistemperature may vary within the range of from 1500 to 1700" F., althoughthe lower temperature ranges of from 1550 to 1650 arepreferable. Thesame will of course be tru of the heat treating furnaces 17 and 23.

The advantages of the present invention arise not only by reason of thenew article of manufacture capable of production in accordance with myinvention, but from the adaptability of a cold rolling process to theproduction of ferrous materials for electrical purposes.

This application claims my improved product generically and certainspecies thereof. My application, Serial No. 688,410, filed September 6,1933, claims that range of silicon steels coming under my invention andhaving a silicon content of 2.75 to 3.5%, which range has herein beenclassified as special dynamo grade. My improved silicon steels which areclassified herein as transformer grades, and comprehending a siliconrange of 3% or more, are specifically covered by my copendingapplication Serial No. 688,411, filed September 6, 1933.

While for purposes of a better understanding of the invention, I haveindicated more or less diagrammatically different forms of apparatus anddifferent steps which may be utilized in accordance with the invention,together with different silicon contents, reductions, thicknesses andtime-temperature treatment conditions, it will be apparent to thoseskilled in the art that changes in all of these respects may be made inthe manner indicated herein without departing either from the spirit ofmy invention or the scope of my broader claims.

I claim:

1. In the method of making silicon steel, the steps consisting ineffecting a heavy reduction by cold work, heating the metal to remove atleast a part of the strain, cooling it and then annealing it, the metalhaving some strain therein at the commencement of such annealing.

2. In the method of making silicon steel, the steps consisting ineffecting a heavy reduction by cold work, heating the metal to removepart but not all of the strain thus imparted, cooling the metal, andthen annealing it.

3. In the method of making silicon steel, the steps consisting ineffecting a heavy reduction by cold work, heating the metal to removepart but not all of the strain thus imparted, cooling the metal,annealing it, allowing it to'cool after such annealing to a point whereit will not acquire a coil set upon coiling, and then coiling it.

4. As a new article of manufacture, electrical steel in sheet-like formcontaining .3-6% silicon and having electrical properties characteristicof those obtained when a steel of substantially the same siliconcontent, within such range, is subjected to heavy reduction by coldwork, followed by heating to remove part but not all of the strain thusimparted, cooling, and then annealing.

5. As a new article of manufacture, electrical steel in sheet-like formcontaining .3-6% silicon and having electrical properties characteristicof 'those obtained when a steel of substantially the same siliconcontent, within such range, is subjected to heavy reduction by coldwork, followed by heating to remove part but not all of the strain thusimparted, cooling, and then annealing with in a temperature range offrom 1500 to 1700 F.

6. As a new article of manufacture, electrical steel in sheet-like formcontaining .3-6% silicon and having electrical properties characteristicof those obtained when a steel of substantially the same siliconcontent, within such range, is hot rolled into a strip substantiallyfree from cold working strains, then subjected to heavy reduction bycold work, then heated to remove part but not all of the strain thusimparted, then cooled, and then annealed.

7. As a new article of manufacture, electrical steel containing .3-6%silicon and having electrical properties characteristic of thoseobtained when a steel of substantially the same silicon content, withinsuch range, is subjected to heavy reduction by cold work, followed byheating to remove part but not all of the strain thus imparted, cooling,and then annealing, the steel being in. the form of a strip as that termis used in the metal rolling art.

8. As a new article of manufacture, electrical steel in sheet-like formcontaining .36% silicon and having electrical properties characteristicof, those obtained when a steel of substantially the same siliconcontent, within such range, is subjected to heavy reduction by coldwork, followed by heating to remove part but not all of the strain thusimparted, cooling, and then annealin the steel'being in the form of astrip and having a length in excess of that obtainable by pack rolling.

9. As a new article of manufacture, electrical steel in sheet-like formcontaining .36% silicon and having electrical properties characteristicof those obtained when a steel of substantially the same siliconcontent, within such range, is subjected to heavy reduction by coldwork, followed by heatng to remove part but not all of the strain thusimparted, cooling, and then annealing, the steel being in the form of acoiled strip and further characterized by substantial freedom from coilset.

10. As a new article of manufacture, electrical steel in sheet-like formcontaining .3-6% silicon and having electrical properties characteristicof those obtained when a steel of substantially the same siliconcontent, within such range, is formed by hot roll'ng to strip formsubstantially free of cold working strains having a thickness ofapproximately .0625 inches, cold rolling to approximately .024 inches or61%, passed through a furnace having a temperature of approximately 1900F., the total heating time being such as to remove the undes?rablestrain component in the steel, that is to say, about two minutes in thecase of a steel whose silicon content is approximately l%, andincreasing as the silicon content increases, then cooling and thenannealing, the steel being in the form of a strip as that term is usedin the metal rolling art.

11. As a new article of manufacture, electrical steel in sheet-like formcontaining .3-6% silicon and having electrical properties characteristicof those obtained when a steel of substantially the same siliconcontent, within such range, is formed by hot rolling to strip formsubstantially free of cold working strains having a thickness ofapproximately .0625 inches, cold rolling to approximately .024 inches or61%, passed through a furnace having a temperature of approximately 1900F., the total heating time being such as to remove the undesirablestrain component in the steel, that is to say, about two minutes in asteel whose silicon content is approximately 1%, and increasing as thesilicon content increases, then cooling, and then annealing by heatingto a temperature of 1500-1700 F. and cooling, the steel being in theform of a strip as that term is used in the metal rolling art.

12. As a new article of manufacture, electrical steel in the form ofstrip, containing from .3% to silicon and having electrical propertiescharacteristic of those obtained when a steel of substantially the samesilicon content, within such range, is subjected to heavy reduction bycold work followed by heating to remove part but not all of the strainthus imparted, cooling, and then annealing, the watt loss property ofsuch strip being not more than about 2.8 watts per pound in 22 gaugethickness and decreasing as the silicon content increases, and alsodecreasing as the thickness of the strip decreases.

13. As a new article of manufacture, electrical steel in the form ofstrip, containing from .3 to .7% silicon and having electricalproperties characteristic of those obtained when a steel ofsubstantially the same silicon content, within such range, is subjectedto heavy reduction by cold work followed by heating to remove part butnot all of the strain thus imparted, cooling, and then annealing, thewatt loss property of such strip being not more than about 2.8 watts perpound in 22 gauge thickness, and decreasing as the thickness of thestrip decreases.

14. As a new article of manufacture, electrical steel inthe form ofstrip, containing from 375% to 1.5% silicon and having electricalproperties characteristic of those obtained when a steel ofsubstantially the same silicon content, within such range, is subjectedto heavy reduction by cold work followed by heating to remove part butnot all of the strain thus imparted, cooling, and then annealing, thewatt loss property of such strip being not more than about 2.3 watts perpound in 22 gauge thickness, and decreasing as the thickness of thestrip decreases.

15. As a new article of manufacture, electrical steel in the form ofstrip, containing from 2% to 3% silicon and having electrical propertiescharacteristic of those obta ned when a steel of substantially the samesilicon content, within such range, is subjected to heavy reduction bycold work followed by heating to remove part but not all of the strainthus imparted, cooling, and then annealing, the watt loss property ofsuch strip being not more than about 1.3 watts per pound in 24 gaugethickness, and decreasing as the thickness of the strip decreases.

EDWARD M. FREELAND.

